In situ hybridization studies on murine catalase mRNA expression during embryonic development

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Abstract
In situ hybridization using nucleic acid probes was used to detect cell‐ and tissue‐specific transcript(s) of embryonic genes during development and differentiation. This highly sensitive technique has the potential to provide valuable information on the regulation of low‐abundance housekeeping genes during development. We have determined the experimental conditions required to detect the catalase message in adult mouse liver. Catalase effects the breakdown of H2O2 to O2 and H2O and offers protection against the toxic effects of oxygen radicals. We used a cloned 550 bp BamHI‐Pstl fragment from a mouse catalase cDNA (pMCT‐1) to generate 35S‐labeled sense and antisense riboprobes. The experimental conditions used were sensitive enough to quantitate the abundance of silver grains generated by the antisense riboprobe on the adult liver, a tissue known to be positive for this message. The hybridization protocol was applied to serial sections of 13‐ and 18‐day‐old mouse embryos. The results suggest that the catalase expression in the liver and brain begins with somite formation and increases with development and differentiation. On the other hand, this message appears to be absent in mesenchyme, particularly in day 13 embryos. The message in positive tissues appears evenly distributed throughout the cell. The observed expression of the catalase message in the adult liver is approximately six times that in the embryonic liver. It is compatible with the enzyme activity results and emphasizes the sensitivity of the in situ hybridization method (over northern blot, etc.) used in this study.